Anyone? :cry:
Studio build in Wales, UK...again!
Originally posted at johnlsayers.com, topic 21409.
The overall idea is fine, but there's some details that need ironing out...
1) Remove the central baffle, directly in front of the inlet duct: it is not doing you any good at all, and in fact is creating additional friction that you do not need.
2) It does not look like the cross sectional area inside the silencer remains roughly constant, and it does not seem to be at least twice the area of the ducts.
3) What happens on the two outboard ends? It seems you plan to attach duct there? Think about that... the silencer won't be doing anything at all if the air that goes into it through one duct, then comes out of it again and through other ducts that are inside the same noisy place it was before...
- Stuart -
I am exhausted right now, but I'm not understanding the issue with the Y splitter design here other than the issues your pointed out in points 1 and 2. Can someone please make this more clear for me to understand?3) What happens on the two outboard ends? It seems you plan to attach duct there? Think about that... the silencer won't be doing anything at all if the air that goes into it through one duct, then comes out of it again and through other ducts that are inside the same noisy place it was before...
Probably one of the middle two images would provide the best circulation.1. I've drawn up some ideas for the control room, blue being my supply of fresh air and red being my returns. Would some of these ideas work? If so, which of these locations would be best for my return ducts?
The silencer boxes provide insertion loss but also maintain the mass as you're penetrating your leaf. Nothing to do with the vent grilles unless you're using the silencer as an actual inlet/outlet to your room with no duct work running in your room.3. I know I need a silencer box for both the supply and return on both leaves, (4 boxes) but do I also need a box for each vent?
Yes.4. Do the silencer boxes need to have the same equivalent amount of mass as my walls?
Flex duct works well. PVC won't work well and will cost a fortune. First off, it's best if you use duct lined duct work. Also, you will need quite large duct work to keep your air velocity and pressure drop low. Lastly, I'm not sure how you would connect a grille to PVC.5. I am thinking I should use flex duct in the cavity between my 2 leaves, to join between the outer and inner silencer boxes, and then could I use round PVC pipe for the ducting inside the room?
HVAC is a step learning curve dude. Especially weirdo studio HVAC! I know there are a lot of threads on the forum that should answer most of your questions about it. There are a handful that go through all of the calculations you need to do. Don't freak out too bad when you can't find answers. Please try and do your homework by checking the threads but before you get to the crying stage, just ask your questions here on your thread. I know I almost got to the crying stage as I was researching HVAC! GregOnce I've figured this out I'll need to ask how to work out what size ducting I need as well as the size of the boxes themselves. Now I'm off to learn more about HRVs and how much air needs to be supplied to my room...
Thank-you Stuart. Okay, so something more like this? (see attached) So, as an example if I used a round 4" duct then the cross sectional area would be 12.56" is that correct? Then the cross-sectional area of the passage way through the silencer baffles needs to be constant (i.e. same width and height?) and at least twice that of the duct... So would I measure the width and height of the passageway to work out the area but not the length of the passageway? I am so confused Though I am confident you are correct, I am also confused about what you mean in your last point... the outboard ends of the silencer would connect to ducts, and the end of the ducts would connect to registers, or vents, or whatever you want to call them, inside my hopefully quiet control room... The noisy ventilator would be in a different room, then the supply and return coming directly off of it would go through their own silencers, then through the 2 leaves without rigid connection in the cavity, then into silencers again, then the control room ducts, then the vents in the room. Is this not correct?The overall idea is fine, but there's some details that need ironing out... 1) Remove the central baffle, directly in front of the inlet duct: it is not doing you any good at all, and in fact is creating additional friction that you do not need. 2) It does not look like the cross sectional area inside the silencer remains roughly constant, and it does not seem to be at least twice the area of the ducts. 3) What happens on the two outboard ends? It seems you plan to attach duct there? Think about that... the silencer won't be doing anything at all if the air that goes into it through one duct, then comes out of it again and through other ducts that are inside the same noisy place it was before... - Stuart -
Thanks a lot Greg, yeah for sure this is a steep learning curve... just like most things in studio design! Regarding sizing the ducts and duct material, this is what I found written by Rod on GS: "If your plans are a split system you need to think this though a bit more. First off - how did you determine system size? Is your space well isolated from the outside world? If the answer is "yes" then that would also mean it is well insulated - and in that case the thermal looses might be small enough that an over-sized unit will never have enough run time to dehumidify to any meaningful degree. By the same token - an undersized unit will never get the job done. Proper sizing is key here. You already know you want to keep velocity down - no way you want to exceed 300 fpm (feet per minute) at the inlet to the space - and preferably 100 fpm (that's always the design goal I shoot for if space permits) But velocity outside of that is not really important - so you can decrease duct size outside of the isolation box as long as you deal with it at the box. That minimizes duct costs. I never (ever) design systems using flex duct except for a very short length of flex at the box to decouple one side of the box/room from the air handler. I'm pretty sure I mentioned this in the book." So it seems that I should use rigid duct in the actual rooms, but flex duct in the cavity. What type of rigid ducting would you recommend? Galvanized metal? And would round be better than rectangular? Also, from what Rod has said, the ducting coming out of the silencers in the control room can be small so long as the silencer brings the velocity down... so would that mean the silencer box needs to double the cross sectional area of the duct work feeding it? (from the ventilator) If I say there would be a maximum of 10 people in the control room (more likely it'll only be 5 or 6, but you never know) then how what do I need to look for in terms of specs for either a fan or HRV? I know that it needs to provide enough fresh air for each person (15cfm) with 6 exchanges per hour, so does that mean I need a fan or HRV that is rated at providing 150cfm? Then, how does the ducting effect it? If I run it through a ducting calculator it says my ducts should be about 8" for a round duct, but does length of duct effect that? how about if you split it into two ducts at 90 degree angles? Then, as Rod says, if you make your silencer big enough you can decrease the size... but by how much? These are the types of questions I need help with, so if you could help I'd really be grateful. PaulI am exhausted right now, but I'm not understanding the issue with the Y splitter design here other than the issues your pointed out in points 1 and 2. Can someone please make this more clear for me to understand?3) What happens on the two outboard ends? It seems you plan to attach duct there? Think about that... the silencer won't be doing anything at all if the air that goes into it through one duct, then comes out of it again and through other ducts that are inside the same noisy place it was before...Probably one of the middle two images would provide the best circulation.1. I've drawn up some ideas for the control room, blue being my supply of fresh air and red being my returns. Would some of these ideas work? If so, which of these locations would be best for my return ducts?The silencer boxes provide insertion loss but also maintain the mass as you're penetrating your leaf. Nothing to do with the vent grilles unless you're using the silencer as an actual inlet/outlet to your room with no duct work running in your room.3. I know I need a silencer box for both the supply and return on both leaves, (4 boxes) but do I also need a box for each vent?Yes.4. Do the silencer boxes need to have the same equivalent amount of mass as my walls?Flex duct works well. PVC won't work well and will cost a fortune. First off, it's best if you use duct lined duct work. Also, you will need quite large duct work to keep your air velocity and pressure drop low. Lastly, I'm not sure how you would connect a grille to PVC.5. I am thinking I should use flex duct in the cavity between my 2 leaves, to join between the outer and inner silencer boxes, and then could I use round PVC pipe for the ducting inside the room?HVAC is a step learning curve dude. Especially weirdo studio HVAC! I know there are a lot of threads on the forum that should answer most of your questions about it. There are a handful that go through all of the calculations you need to do. Don't freak out too bad when you can't find answers. Please try and do your homework by checking the threads but before you get to the crying stage, just ask your questions here on your thread. I know I almost got to the crying stage as I was researching HVAC! GregOnce I've figured this out I'll need to ask how to work out what size ducting I need as well as the size of the boxes themselves. Now I'm off to learn more about HRVs and how much air needs to be supplied to my room...
I will bet my life savings that your room needs a way bigger duct than a 4" RD feeding your silencer. I didn't look to see how big your room is but you probably need an 8 or bigger. Here is my answer for your cross sectional area question copy/pasted from my notes: Cross sectional areas of common duct: Area of a circle = π r2 Radius = half of the diameter Duct CSA: 4” RD duct = 12.57 sq in. Double = 25.14 sq in. 5” RD duct = 19.63 sq in. Double = 39.26 sq in. 6” RD duct = 28.27 sq in. Double = 56.54 sq in. 8” RD duct = 50.27 sq in. Double = 100.53 sq in. 9” RD duct = 63.62 sq in. Double = 127.23 sq in. 10” RD duct = 78.54 sq in. Double = 157.08 sq in. 12” RD duct = 113.1 sq in. Double = 226.19 sq in. Area of a rectangle = width x height Area of a oval duct = major radius x minor radius x π This is for a true oval, not a flat oval like HVAC duct though :-S Area of flat oval = π (minor radius)2 + [(major diameter- minor diameter) x minor diameter)] OR [(π minor 2) / 4] + 3 (major - minor) To answer your question about the path inside your silencer, it needs to at LEAST double in cross sectional area. It certainly does not have to be a square (equal height and width) path. However, the more square it is, the less pressure drop with be introduced which is very important in your design. Addressing your comment regarding a constant size, the CSA within the silencer can change. Actually, the more changes, the more attenuation. However, realize that with each CSA change, a pressure drop is realized. Remember, the larger the CSA change, the more the attenuation. So, on your Y split type box, I would double the CSA on each half. This would essentially quadruple the CSA of the inlet. This will also really slow down your air velocity, reduce the static pressure drop and reduce the air movement noise within the box.So, as an example if I used a round 4" duct then the cross sectional area would be 12.56" is that correct? Then the cross-sectional area of the passage way through the silencer baffles needs to be constant (i.e. same width and height?) and at least twice that of the duct... So would I measure the width and height of the passageway to work out the area but not the length of the passageway? I am so confused
So, you are using a forced air ducted system? Not a ductless mini split? Your statement seems to be correct.The noisy ventilator would be in a different room, then the supply and return coming directly off of it would go through their own silencers, then through the 2 leaves without rigid connection in the cavity, then into silencers again, then the control room ducts, then the vents in the room. Is this not correct?
Once it's in your room, you can use whatever you want. RD always has the least friction coefficients. Rect allows you to maximize space. Remember, inside your room you should always use duct liner.So it seems that I should use rigid duct in the actual rooms, but flex duct in the cavity. What type of rigid ducting would you recommend? Galvanized metal? And would round be better than rectangular?
You've misunderstood his point. I'll try to explain this better: The CFM is a constant throughout a duct run. Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2 So, if CFM is a constant, then the velocity changes depending on the CSA. So, if you have a smaller duct, your velocity will increase. If you use larger ducts, your velocity decreases. In your room, you need to achieve a maximum of 300 feet per minute at your register/grille. So yes, you COULD use smaller duct inside your room as long as you make your CSA large enough to reduce the air velocity before it hits your register/grille. However, you will increase your pressure drop and air noise inside those ducts. Duct liner will help with the air noise. Most importantly, you want to deal with turbulence noise introduced by any change of direction or CSA change. You could use a conical transition which would not allow you to gain the immediate CSA change (insertion loss achieved by a gross impedance mismatch). A gradual change in CSA like a cone (or wave guide) provides will prevent distortion or turbulence, the true rule of thumb is that you need a certain distance between any direction change or CSA change and the mouth of your grille/register. I've heard two values for this distance. It's either 3 or 5 times the diameter of that which is feeding the grille/register. So let's say your have a 4" round duct that goes to a required 6" round grille, you'd need a distance of between 12 and 20" of straight duct to prevent noise at the mouth.Also, from what Rod has said, the ducting coming out of the silencers in the control room can be small so long as the silencer brings the velocity down... so would that mean the silencer box needs to double the cross sectional area of the duct work feeding it? (from the ventilator)
Purely for the required 30% fresh air circulation, you can figure it out like this: Flow rate in CFM = ft3/min = [# of air changes per hour X cubic volume of room] / 60 min # of air changes must be at least 6 changers per hour Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2 This is actually expressed as v=q/A Air velocity must be less than 300 ft/min for studios So, if you need 30% fresh air, take your total CFM and calculate 30% of it. That would be your fresh air CFM. Size your HRV or fan based off of that. Sizing your actual air handler unit is a different story though as you need to need to figure out your sensible and latent loads.If I say there would be a maximum of 10 people in the control room (more likely it'll only be 5 or 6, but you never know) then how what do I need to look for in terms of specs for either a fan or HRV? I know that it needs to provide enough fresh air for each person (15cfm) with 6 exchanges per hour, so does that mean I need a fan or HRV that is rated at providing 150cfm?
Typical duct sizing calculators assume a 0.1 friction rate. You can use these to calculate your runs from your air handler to your silencer boxes. From the boxes to your register/grilles you need to size these based on your velocity and CSA changes. Once you've sized everything this way, you need to calculate your total static pressure. If your blower will not run within your system pressure, you may have to change your duct sizing from the air handler to the silencer boxes and then ultimately, that may change everything down the line!Then, how does the ducting effect it? If I run it through a ducting calculator it says my ducts should be about 8" for a round duct, but does length of duct effect that?
That introduced a pressure drop. These are the things you calculate later to determine your total static pressure. Using 1.5x radius bends instead of 1x can help as well. To be honest with you, I made my own spreadsheet to calculate this because I could find no good resources online. It's a chore and takes hours to calculate :cry:how about if you split it into two ducts at 90 degree angles?
Again, changing the CSA achieves insertion loss. As I mentioned before, it has negative side effects as well. Another reason to have a large CSA throughout your box is because all of those sharp corners introduce a ton of static pressure. The bigger the path, the less pressure drop!Then, as Rod says, if you make your silencer big enough you can decrease the size.
If you look at this picture, you'll see that even when we double or halve the CSA, we aren't achieving great levels of insertion loss. That's why I suggest that you double each half of your Y box so that you are quadrupling your CSA! These sort of details are the ones you have to make informed decisions on while designing your studio! Greg.. but by how much? These are the types of questions I need help with, so if you could help I'd really be grateful.
Greg - amazing info, thanks so much for the detailed reply. I want to digest it all a bit more before I reply as it's a lot to take in.
Thanks again,
Paul
Okay so I've had a good read over your reply Greg, I'm starting to understand it (i think). Just before I go on I want to check that I am measuring CSA correctly in my baffle box, is it as shown in my diagram? (in red)I will bet my life savings that your room needs a way bigger duct than a 4" RD feeding your silencer. I didn't look to see how big your room is but you probably need an 8 or bigger. Here is my answer for your cross sectional area question copy/pasted from my notes: Cross sectional areas of common duct: Area of a circle = π r2 Radius = half of the diameter Duct CSA: 4” RD duct = 12.57 sq in. Double = 25.14 sq in. 5” RD duct = 19.63 sq in. Double = 39.26 sq in. 6” RD duct = 28.27 sq in. Double = 56.54 sq in. 8” RD duct = 50.27 sq in. Double = 100.53 sq in. 9” RD duct = 63.62 sq in. Double = 127.23 sq in. 10” RD duct = 78.54 sq in. Double = 157.08 sq in. 12” RD duct = 113.1 sq in. Double = 226.19 sq in. Area of a rectangle = width x height Area of a oval duct = major radius x minor radius x π This is for a true oval, not a flat oval like HVAC duct though :-S Area of flat oval = π (minor radius)2 + [(major diameter- minor diameter) x minor diameter)] OR [(π minor 2) / 4] + 3 (major - minor) To answer your question about the path inside your silencer, it needs to at LEAST double in cross sectional area. It certainly does not have to be a square (equal height and width) path. However, the more square it is, the less pressure drop with be introduced which is very important in your design. Addressing your comment regarding a constant size, the CSA within the silencer can change. Actually, the more changes, the more attenuation. However, realize that with each CSA change, a pressure drop is realized. Remember, the larger the CSA change, the more the attenuation. So, on your Y split type box, I would double the CSA on each half. This would essentially quadruple the CSA of the inlet. This will also really slow down your air velocity, reduce the static pressure drop and reduce the air movement noise within the box.So, as an example if I used a round 4" duct then the cross sectional area would be 12.56" is that correct? Then the cross-sectional area of the passage way through the silencer baffles needs to be constant (i.e. same width and height?) and at least twice that of the duct... So would I measure the width and height of the passageway to work out the area but not the length of the passageway? I am so confusedSo, you are using a forced air ducted system? Not a ductless mini split? Your statement seems to be correct.The noisy ventilator would be in a different room, then the supply and return coming directly off of it would go through their own silencers, then through the 2 leaves without rigid connection in the cavity, then into silencers again, then the control room ducts, then the vents in the room. Is this not correct?Once it's in your room, you can use whatever you want. RD always has the least friction coefficients. Rect allows you to maximize space. Remember, inside your room you should always use duct liner.So it seems that I should use rigid duct in the actual rooms, but flex duct in the cavity. What type of rigid ducting would you recommend? Galvanized metal? And would round be better than rectangular?You've misunderstood his point. I'll try to explain this better: The CFM is a constant throughout a duct run. Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2 So, if CFM is a constant, then the velocity changes depending on the CSA. So, if you have a smaller duct, your velocity will increase. If you use larger ducts, your velocity decreases. In your room, you need to achieve a maximum of 300 feet per minute at your register/grille. So yes, you COULD use smaller duct inside your room as long as you make your CSA large enough to reduce the air velocity before it hits your register/grille. However, you will increase your pressure drop and air noise inside those ducts. Duct liner will help with the air noise. Most importantly, you want to deal with turbulence noise introduced by any change of direction or CSA change. You could use a conical transition which would not allow you to gain the immediate CSA change (insertion loss achieved by a gross impedance mismatch). A gradual change in CSA like a cone (or wave guide) provides will prevent distortion or turbulence, the true rule of thumb is that you need a certain distance between any direction change or CSA change and the mouth of your grille/register. I've heard two values for this distance. It's either 3 or 5 times the diameter of that which is feeding the grille/register. So let's say your have a 4" round duct that goes to a required 6" round grille, you'd need a distance of between 12 and 20" of straight duct to prevent noise at the mouth.Also, from what Rod has said, the ducting coming out of the silencers in the control room can be small so long as the silencer brings the velocity down... so would that mean the silencer box needs to double the cross sectional area of the duct work feeding it? (from the ventilator)Purely for the required 30% fresh air circulation, you can figure it out like this: Flow rate in CFM = ft3/min = [# of air changes per hour X cubic volume of room] / 60 min # of air changes must be at least 6 changers per hour Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2 This is actually expressed as v=q/A Air velocity must be less than 300 ft/min for studios So, if you need 30% fresh air, take your total CFM and calculate 30% of it. That would be your fresh air CFM. Size your HRV or fan based off of that. Sizing your actual air handler unit is a different story though as you need to need to figure out your sensible and latent loads.If I say there would be a maximum of 10 people in the control room (more likely it'll only be 5 or 6, but you never know) then how what do I need to look for in terms of specs for either a fan or HRV? I know that it needs to provide enough fresh air for each person (15cfm) with 6 exchanges per hour, so does that mean I need a fan or HRV that is rated at providing 150cfm?Typical duct sizing calculators assume a 0.1 friction rate. You can use these to calculate your runs from your air handler to your silencer boxes. From the boxes to your register/grilles you need to size these based on your velocity and CSA changes. Once you've sized everything this way, you need to calculate your total static pressure. If your blower will not run within your system pressure, you may have to change your duct sizing from the air handler to the silencer boxes and then ultimately, that may change everything down the line!Then, how does the ducting effect it? If I run it through a ducting calculator it says my ducts should be about 8" for a round duct, but does length of duct effect that?That introduced a pressure drop. These are the things you calculate later to determine your total static pressure. Using 1.5x radius bends instead of 1x can help as well. To be honest with you, I made my own spreadsheet to calculate this because I could find no good resources online. It's a chore and takes hours to calculate :cry:how about if you split it into two ducts at 90 degree angles?Again, changing the CSA achieves insertion loss. As I mentioned before, it has negative side effects as well. Another reason to have a large CSA throughout your box is because all of those sharp corners introduce a ton of static pressure. The bigger the path, the less pressure drop!Then, as Rod says, if you make your silencer big enough you can decrease the size.If you look at this picture, you'll see that even when we double or halve the CSA, we aren't achieving great levels of insertion loss. That's why I suggest that you double each half of your Y box so that you are quadrupling your CSA! These sort of details are the ones you have to make informed decisions on while designing your studio! Greg.. but by how much? These are the types of questions I need help with, so if you could help I'd really be grateful.
That's PART of it, yes. But that's just the area at the tip of the baffle. The air also flows up the sides of the baffle, between it and the next baffle... - Stuart -Just before I go on I want to check that I am measuring CSA correctly in my baffle box, is it as shown in my diagram? (in red)
Hmm... okay, now I'm more confused. By that logic, surely the air travels through the entire silencer box.. so do I just measure the total area of the pathway between the baffles? What defines the cross sectional area compared to the total area?That's PART of it, yes. But that's just the area at the tip of the baffle. The air also flows up the sides of the baffle, between it and the next baffle... - Stuart -Just before I go on I want to check that I am measuring CSA correctly in my baffle box, is it as shown in my diagram? (in red)
You seem to not be getting the point I was making: You need to measure the cross sectional area in SEVERAL places, and make sure that it remains reasonably constant throughout. There can be changes, yes, but you don't want to create bottle-necks where you force a very high speed and very low pressure through a small cross-section, then have it widen out to a much larger area, forcing the air to slow down and suddenly increasing the pressure. That large change only needs to happen in a couple of spots, not frequently throughout. Every time you have a large change in pressure and velocity, there is energy loss, which implies a higher static pressure, and a larger fan.
- Stuart -
Okay, I see. I guess that's where I'm confused as though it may not be clear in my design, the width and height throughout my pathway is indeed constant.
So, providing I have a cross sectional area that is at least double (ideally, even more) the cross sectional area of my ducting, then a design like this (a 'y' split') could work?
If yes, then I'll do the following next:
- Spec a HRV that provides the right amount of fresh air at the correct velocity
- Size the duct work accordingly
- Size the silencer boxes to at least double the cross sectional area of the ducting
- Find registers rated below NC20
Paul
:thu:
- Stuart -
This means calculating your systems static pressure. Check the sticky at the top of the design forum I started. There has been some great info posted there. I hope to find some time to post more helpful stuff in that thread. Greg- Spec a HRV that provides the right amount of fresh air at the correct velocity
I just noticed that thread, it's very informative, thanks for sharing it! I found this written by Rod Gervais: "Fresh air supply systems have to do with the number of people in the room - not the volume of the room. Picture it this way to get your head around the concept: In a room that was 6' wide - by 6' deep - with 8' high ceilings you could comfortably put 1 person (perhaps 2 if they really REALLY liked each other ).......... that wouldn't suddenly change simply because those ceilings were 40' instead of 8'. 15cfm per person would be a minimum fresh air supply......... So figure out the maximum number of people that will be in the room - and derive the volume by multiplying the total by 15 (or 20 if you want a little buffer) Once you know the volume of air you need - you need to then choose a fan capable of providing that volume........ When it comes to choosing the fan don't let yourself be fooled into thinking that a computer fan can provide that air.......... I don't say this to imply you would - simply a comment because I see a lot of people who believe they will....... thus I mention it just as an aside. Whatever fan you choose will have specifications (available) that not only tell you the volume of air they provide - but also the velocity that air is going to be traveling as it leaves the fan......... and everything is about the combination of those 2 elements when it comes to figuring this out. As a general rule - I would not concern myself (if I were you) about trying to calculate friction loss in the duct work (friction loss doesn't really come into play until after the first 100 of straight duct - or combination of straight duct/elbows that equal 100 of straight duct due to additional losses in those elbows) I would also avoid (like the plague) using any of the flex duct products for long runs..... in the case of flex duct friction loss does come into play much quicker than rigid duct systems - you'll always do better with rigid duct. OK - so you know your fan size - and you've figured out the duct size you can use to make it from point "A" (which is the fan) to point "B" (your inlet location in the room) - and the corresponding size/location for the outlet in the room (point "C") back to the outside world (point "D") That would be the total duct length you have to consider for the fan. OK - so you know the fan size - you know the volume - you sized the duct (so you know the velocity) and now you want to get the air into/out of the room. As far as location goes - as long as you have at least 4' between the inlet/outlet for the system I would not worry about short cycling the air - note that if you are forced to put the isolation boxes side by side you can deal with that vertically. Determining the size of your boxes is not that difficult........ you want to get the volume of air into the room while decreasing velocity to less than 300fpm, if you have the room 100fpm is a great target goal. You should use at least 3 baffles inside of the iso-box - these force the air to turn corners which blocks outside noise from making it's way through the box.. The last piece of the puzzle is the grille - I always specify grilles manufactured by Nailor Industries - they are a bit pricy - but you have a ton of testing done on their products from the perspective of acoustics....... and you can then choose exactly the right grille/louver for your velocity (in a perfect world pick a louver with an NC-0 rating - but never a rating higher than NC-20) However as long as the manufacturer can provide with you with test data any manufacture's grilles should work just as well......... Avoid cheap grilles with no data - they will most probably be very noisy A cheap grille forms an added barrier to air flow - a bottle neck if you will - and (as such) that can be a point of introducing noise - which is what you have been trying to avoid all along with proper sizing and baffle design....... I hope this helped, Rod" So he's saying it's best to work out the required air supply based on the amount of people that'll likely be in the room(s), but I noticed in your previous reply you mentioned working it out based on the 30% minimum. If I worked it out using the amount of people then if I said there is going to be 10 people then it would be: 10 x 15cfm = 150cfm If I worked out using the 30% minium fresh for my room volume with 6 air changes per hour then it would be: 23.92 x 19.57 x 11 x 6 = 30,895.55 30,895.55 / 60 = 514.93 30% of 514.93 = 154.48cfm So, very similar numbers. I just want to check with you that I have done that all right, and therefore I need to spec a fan/HRV that can provide that amount of cfm? In the UK we use the metric system and I am only see specs in m3/h, things like this: Extract Air Performance: Boost – 100 m3/hour Trickle – 30 m3/hour Intake Air Performance: Boost – 100 m3/hour Trickle – 30 m3/hour which means I need to convert my cfm to m3/h: 154.48cfm x 60 = 9268.8 9268.8 = 262.46 m3/h Have I worked that out correctly? PaulThis means calculating your systems static pressure. Check the sticky at the top of the design forum I started. There has been some great info posted there. I hope to find some time to post more helpful stuff in that thread. Greg- Spec a HRV that provides the right amount of fresh air at the correct velocity
Looks good!
Greg
Hi again guys,
I would appreciate some help regarding the triple leaf effect. I have read the threads on here as well as the Wyle paper and though I understand some of it, I am not clever enough to understand the more complex maths.
My thinking is related to my build; as I am building my studio in stages, starting with the inner inside out leaf of the control room, my plan is to construct the outer leaf as well as all the other rooms at a later stage when I have the money and time to do so.
That has complicated things for many reasons, but it means I need to be extra vigilant (don't we all) right now while in the planning stage.
Now to my question: I know that putting a dividing wall in between a double wall assembly is generally not a good idea if you want maximum low frequency isolation, as it splits the air gap up into smaller cavities, changing the frequency at which the wall assembly isolates down to etc etc... so in layman's terms, a triple leaf wall assembly constructed of the same materials with the same overall thickness as the equivalent double wall assembly would perform worse at low frequencies than the double wall assembly.
But what if after constructing a double wall assembly, with a nice big air gap, and which isolates effectively as required all the way down you then construct another wall in front of it with another big air gap and extra materials? In other words, the new triple leaf assembly's initial air gap would be the same as the original double wall assembly, but with another added air gap and more mass on the other side.
Why am I asking this?
I was wondering if I could build my control room fully isolated now, and then at a later date add on the live room and other rooms without needing to demolish the one wall in question. The wall that I'd need to demolish would be supporting the outer leaf roof, and so it would not be a simple task. I would build my outer leaf with concrete blocks, and my inner leaf is timber frame.
If it is not a good idea to use this triple wall then I will just have to make do with a single leaf structure for the time being, but if it either a) improves isolation or b) performs as good a double wall, then it would be a nice way to go for me.
I have attached some drawings of what I had in mind with some calculations:
Marked in red is the triple wall in question. Control room to the left, live room to the right. My original floor plan does not have this assembly, there are only two decoupled walls. Concentrating just on the control room, if I built a concrete block wall all the way around the inner timber leaf, then for the time being that room would be completely isolated, then I could add on and extend with the other rooms later.
This triple leaf design would maintain the exact same air gap between the first and second leaves, but introduces a third leaf. This means it takes up more space, which eats in to the side of my live room. The ceilings for the control room and live rooms would be supported on the inner leaves of each room and the roof the whole building would be supported on the outer block walls as well as this middle concrete block wall.
The double wall option would be like this:
The triple wall option would be like this:
And here's the calculations separately for both the control room side of the triple leaf assembly, and the live room side of the assembly:
Control Room Side
Live Room Side
And here's the data for just the double leaf option:
I can calculate the wall assemblies for a double leaf properly, but I do not know how to calculate for a triple leaf assembly properly, maybe someone much cleverer than me can calculate it for me based on the info I've given here?
Paul
Cool to see you're finding the calculator useful! I was wanting to make a three leaf version of it sometime. I actually started on it, but it's much more daunting than a two leaf and I'd rather spend any free time I have with my wife and kids. . . I know.... I'm selfish!
Anyway, I fully understand your dilemma and as much as I appreciate your efforts and desire for killer isolation, if appears with your concrete leaf, you're going to be limited by flanking in your slab. I mean, the values the calculator put out are theoretical assuming your floor is able to provide that level of isolation as well. Also, HVAC insertion loss. Having said that, I can confidently say that your three leaf system will be fine for what you're doing. If you didn't have concrete, it'd be a different story.
Greg
Incredibly selfish... how dare you :lol:Cool to see you're finding the calculator useful! I was wanting to make a three leaf version of it sometime. I actually started on it, but it's much more daunting than a two leaf and I'd rather spend any free time I have with my wife and kids. . . I know.... I'm selfish!
Thanks Greg, that's very good to know. I wonder, could I even expect better isolation with the concrete leaf in the middle? For what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building. PaulAnyway, I fully understand your dilemma and as much as I appreciate your efforts and desire for killer isolation, if appears with your concrete leaf, you're going to be limited by flanking in your slab. I mean, the values the calculator put out are theoretical assuming your floor is able to provide that level of isolation as well. Also, HVAC insertion loss. Having said that, I can confidently say that your three leaf system will be fine for what you're doing. If you didn't have concrete, it'd be a different story.
I bet you meant to say that each leaf will be built on it's own slab.. ?? If so, that's awesome and will certainly improve your isolation. GregFor what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building.
Whoops! Yes, that's exactly what I meant to say, sorry for the typo. Great, thanks for your reassurance. Now back to HVAC... What kind of ducting are you using Greg? Are you using rigid or flex duct? PaulI bet you meant to say that each leaf will be built on it's own slab.. ?? If so, that's awesome and will certainly improve your isolation. GregFor what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building.
Sheet metal except between a two of the silencer boxes I plan to use flex duct. That will be like 4 feet or so. For between all of my other silencers, I'll join the MDF sleeves using a product from this company: http://www.durodyne.com/connector.php GregWhat kind of ducting are you using Greg? Are you using rigid or flex duct?
Just a quick question: Has anyone ever used this product?
https://www.insulationshop.co/british_g ... _19mm.html
19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad.
Thoughts?
It looks like good stuff! GregJust a quick question: Has anyone ever used this product? https://www.insulationshop.co/british_g ... _19mm.html 19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad. Thoughts?
Excellent! The plan is to use a layer of this then a layer of 12.5mm 8kg/m2. Both of these layers will go over the 18mm OSB I have up already, so the total surface density will be around 34kg/m2. According to your calculator this is what will be needed (in conjunction with a 6” airspace and then concrete blocks) to isolate all the way down to the low lows with a tl in the 60s. One thing I was thinking about Greg, is the flex element of panels. Is there any realistic way of either being able to predict what effect that has on increasing TL or compensating for it? PaulIt looks like good stuff! GregJust a quick question: Has anyone ever used this product? https://www.insulationshop.co/british_g ... _19mm.html 19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad. Thoughts?